This invention relates to a method and apparatus for monitoring the conditions on and in the neighborhood of the distal end of a fiber optic within the body of a patient being treated with light (usually from a laser) delivered through this fiber optic, for ablating or otherwise treating tissue at a treatment site within the patient.
In conventional methods for monitoring such conditions, laser light is transmitted from a laser to the treatment site via a first fiber optic, known as a jumper, and a second fiber optic, which may be referred to as a treatment fiber and which has its proximal end optically coupled to the jumper and its distal end positioned at the treatment site within the patient. Typically, the jumper is smaller in diameter than the treatment fiber.
In such treatment, light is scattered (such as by fluorescence) from tissue at the treatment site, and is monitored for determining the status of tissue at the site. An example of such treatment is described in applicants' U.S. Pat. No. 5,111,821 issued May 12, 1992 entitled "In Vivo Fluorescence Photometer," by William R. Potter, which is incorporated herein by reference. The light which is scattered by the tissue at the treatment site may be monitored by using a directional tap on the jumper.
Fiber optic delivery systems of conventional design which are used in clinical photodynamic therapy (PDT) utilize a long (10-30 meter), 100 um-core quartz fiber (i.e., the jumper) which conducts light from a dye laser to the treatment room in a hospital. The distal end of the jumper (i.e., the end farther from the laser) is held against the proximal end of a 400 um core treatment fiber, utilizing conventional SMA-type connectors and other hardware as necessary. Light is thus transferred to the treatment fiber.
The treatment fiber is usually about 2 meters long, and its distal tip is modified to provide the required light distribution. Light may be required to escape in a uniform fashion along a prescribed length (typically 0.5 to 4.0 cm), thus forming a cylindrical light source. Alternatively, the treatment may require a source with spherical symmetry ( a "light bulb"), or the fiber may be tipped with a short focal length lens (e.g., 1-3 mm) which projects an image of the fiber tip. Treatment is frequently done through an endoscope.
A drawback to systems presently in use is that continuous monitoring of the fiber tip once it is in the patient has not yet been possible. The usual monitoring technique has been to measure the light leakage from the 100 um core jumper. However, this ensures only that the power in the fiber remains constant, and is not very sensitive to failure of the tip.
It is possible for blood or tissue to carbonize the tip, with a concomitant decrease in the amount of treatment laser light reaching the tumor. Because the eye is not an accurate device for fine discrimination of light levels, a method and apparatus for monitoring the tip of the treatment fiber are needed. Such a method and apparatus are also needed which allow inspection of the fiber tip during actual treatment, which is not possible with conventional designs, because the tip is often embedded in tumor during treatment.